This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Projection-based video units create video images by varying the color and shade of projected light. One example of a projection-based video unit is a digital light processing (“DLP”) system, which employs an optical semiconductor, known as a digital micromirror device (“DMD”) to create video images. Another example of a projection-based video unit is a liquid crystal display (“LCD”) projection system, which projects light through one or more LCD panels to create video images. Many first generation DLP and LCD systems employed a 1:1 correspondence between the resolution of the imaging system and the display resolution. However, it can be expensive to produce DMDs and LCD panels that maintain this 1:1 correspondence while providing higher resolution programming, such high definition television (“HDTV”). For this reason, several techniques have been developed to facilitate the display of video images at resolutions above those natively available from a DMD or LCD panel.
Pixel-shifting is one such resolution-enhancing technique. In pixel-shifting, the light generated by a video imaging system within a video unit, such as a DMD or and LCD, is shifted to focus on more than one pixel locations on a screen. For example, in a DLP system, the light reflected off of one of the micromirrors may be directed at a first pixel location, then at a second pixel location, then back to the first pixel location, and so forth to increase the resolution of the DLP system beyond what is available natively from the DMD. Typically, pixel-shifting is performed by a mechanically modulated projection lens or mirror that can shift between two or more different positions. For example, in a DLP-based system, the projection lens assembly may first direct light from one of the micromirrors on the DMD to the display screen at a first pixel location. After the first pixel has been displayed for a given period of time, the projection lens assembly may be actuated to shine light from the same DMD micromirror at a second pixel location. The projection lens assembly alternates rapidly between the two positions to display each respective pixel. The result is a first and second pixel displayed in separate positions on the display screen.
As will be appreciated, one of the challenges in designing pixel-shifting systems is calibrating the mechanical modulator such that the shifted pixels are displayed in the proper location. Conventional calibration systems either employed an open-loop system wherein the user adjusted the pixel-shifting using a test pattern or employed a closed-loop system that measured the physical movement of the modulator. Disadvantageously, these conventional systems are either unreliable or relatively expensive.
Embodiments of the present invention may relate to an improved system and method for calibrating a pixel shift modulator in a video unit.